. >> he takes legislation that wasn't going to pass civil rights, the tax cut bill and in an in tant johnson gets it moving towards passage. >> thank you very, very, very much. >> chris: last week, caro took part in the library of congress book festival on the national mall and made clear he made johnson come alive for many reader. >> chris: do you like him? >> i don't like him or dislike him. you are in awe of him because you are constantly saying look at what he is doing now. >> chris: he got excited talking about johnson's rise to power but as we turn to the final book he is writing now, his demeanor suddenly changed. >> the story is going to turn very dark as soon as vietnam enters the picture. it is sort of a tragic story. a story of his great dreams that are the destroyed by a war. >> chris: you are 76 now. do you ever worry that you are not going to have time to finish this last book? >> well, sure. but, you know, it is not productive to think like that. >> chris: how long do you think it will take you to finish? >> i could say three or four years but why would you believe me?